Air driven turbines have virtually supplanted all other types of dental handpiece drives. High speed air driven motors are typically located in a drive head which receives the burr or other tool. These motors reach speeds of hundreds of thousands revolutions per minute. However, because the heads need to be sterilized after each use, the operating lives of such heads are relatively short.
There remains a very significant market for so-called "low speed" motors. Such motors are generally located in the grip portion of the handpiece and are connected to the burr in a drive head spaced from the motor through a train of gears and shafts. Such low speed motors can achieve maximum burr speeds on the order of about 20,000 to 40,000 rpm depending upon manufacturer. The speed of such motors typically can be varied by varying the air supplied to the motor typically through a separate foot pedal control coupled with the air supply. However, it is very difficult to vary speed with such foot controls.
In addition, some air driven motors may be provided with speed control valves which limit maximum speed of the motors and even permit reverse rotation of such motors. Due to the miniature size of such motors and the use of air, high precision parts must be used. Alignment of these parts is important to assure smooth operation, long life and minimum air leakage for high efficiency. Moreover, due to their small size and air drives, resolution of the maximum speed of such motors is difficult to achieve. The valving provided to vary air flow must be sufficiently small to fit into the handpiece with the rotor to provide a self-contained unit.